The long-term goals of this proposal are to identify factors that may be related to the increased health and effective functioning of older individuals. Physical activity has been previously shown to affect efficiency of cognitive and motor performance in older adults. These differences in performance are directly related to decreased life satisfaction, restrictions in mobility and social activity, increases in depression, and the incidence of injury due to falls. The proposed project will isolate components of the stimulus-response relationship to determine the exact loci that may be affected by aging and, further, which loci are ameliorated by aerobic fitness. To achieve this goal, a three-stimulus paradigm (S1-S2-S3) will be used to examine event-related potentials (i.e., CNV, SPN, and P3) and reaction time (RT) in four groups of individuals: older and younger physically active and sedentary adults. Previous research has indicated that these evoked potential measures differentially index the stimulus-response relationship, with the SPN reflecting stimulus anticipation, CNV indexing both stimulus orienting and motor preparation, and P3 amplitude and latency reflecting context updating and cognitive processing speed, respectively. The S1 will be a visual warning stimulus that provides information as to whether the upcoming task at S2 will be easy or difficult. S2 will be a discrimination task in which the participant will be instructed to make a decision but to hold their response until the presentation of S3, at which point they will make a choice RT response. It is hypothesized that a main effect for age will occur for all ERP amplitudes (i.e., SPN, CNV, and P3), and latencies (i.e., P3 and RT). It is further hypothesized that physical activity levels will interact with age resulting in increased amplitude and shorter latencies for all measures. It is proposed that the results of this fellowship will aid in advancing our knowledge concerning the health of older adults.